A conventional lock structure 10 in FIG. 1 comprises a handle 11, an escutcheon 12 and a mounting plate 13 covered with the escutcheon 12, wherein the mounting plate 13 comprises a longitudinal slot 13a and a transverse slot 13b, and the escutcheon 12 comprises a protrusion 12a. The protrusion 12a is rotatable in a first direction via the longitudinal slot 13a to make the protrusion 12a constrained inside the transverse slot 13b. The mounting plate 13 can not prevent the escutcheon 12 from rotating toward a second direction opposite to the first direction, once the escutcheon 12 rotates toward the second direction, the escutcheon 12 separates apart from the mounting plate 13 thereby causing the lock structure 10 to be damaged. Besides, a transmission tube (not shown in Figure) of the lock structure 10 is driven to rotate by the handle 11 and actuates a transmission mechanism (not shown in Figure). Once the handle 11 is collided by an external force, the transmission tube and the transmission mechanism are deformed by compression of the handle 11. Thus, the lock structure 10 has failed in operation.